Have you noticed that horsepower and torque have almost become no-brainers? Hot Rod has shown you how to build a 700hp, normally aspirated 502 big-block on pump gas, among other powerful things. With a shot of nitrous or a whiff of blower, mega-power is now mega-easy. But the sole purpose of making all that power is to accelerate your pile of iron up to speed in a ridiculously short amount of time. That assumes, of course, that those poor abused tires can plant all that power to the asphalt. If you have the power, you’re already a resident of Tire Spin City.
While more rubber is a quick fix, it also has to fit under the wheelwell. Assuming you’re not quite ready for tubs and ladder bars, there are some basic tricks that you can apply to improve the launch capabilities of your street/strip stormer. We’ll concentrate on typical V8, rear-wheel-drive cars, and we’ll look at some inexpensive ways to help plant both leaf-spring and coil-spring rear suspensions.
Hammer Down
With the car at full rest, nailing the throttle results in a number of simultaneous vehicle reactions. First, the body tends to pitch upward in the front, moving weight from the front to the rear of the car. That is referred to as weight transfer and improves traction by increasing load to the rear tires. At the same time, most street cars also rotate slightly side to side, moving weight from the left (driver’s) side of the car to the right side. That can be seen by watching a car leave the starting line of the dragstrip from dead astern.
While the body rotates from left to right (clockwise as viewed from the rear), the rear axlehousing rotates in exactly the opposite direction. That counterclockwise rear-axle torque reaction shoves the left rear tire into the pavement while lifting the right rear tire, which explains why nonpositraction-equipped cars always spin the right rear tire. Since unloading the right rear tire can only hurt traction and acceleration, most rear-suspension modifications are aimed at limiting or preventing the rear axle from rotating in this counterclockwise fashion.
There are a couple of tricks you can use to make all this twistin’ and shoutin’ work toward better traction. First, try unbolting the front sway bar from the two lower front control arms. The front sway bar’s job is to transfer weight from the left front to the right front. By disconnecting the sway bar (or better yet, remove it to also eliminate weight), the front end is now able to transfer more weight to the rear tires.
Moving static weight from the front to the rear is another inexpensive way to improve traction. That is the logic behind battery-relocation kits, which take the battery from the front of the car and move it to the right rear where it helps offset the lifting motion of the rear axle. Often, just filling the gas tank can help traction and reduce e.t., even though it increases overall vehicle weight. Ironically, adding a heavy spare tire back into the trunk over the right rear might also result in a quicker e.t.
Hop To It
In leaf-spring cars, wheelhop or axle tramp is caused by the leaf spring “wrapping up” into an S-curve shape as the result of torque input. As the spring hits maximum wrapup, the spring rate also increases radically. At that point, the tire bounces off the pavement and unloads the spring, allowing it to unwind and then rapidly wrap up again. That produces the bouncing effect that not only kills traction but can also tear up U-joints, driveshafts and even transmission extension housing cases. One inexpensive way to reduce axle tramp with leaf-spring cars is to add a second main leaf. Doug Norrdin at Global West Suspension Components typically takes a discarded leaf spring and cuts the spring eyes off the main leaf. The procedure can be performed on any leaf-spring car. Clamping a multileaf spring ahead of the axle centerline is another inexpensive idea that often works.
Weak, factory rubber bushings are often common culprits that contribute to axle tramp. Mushy bushings allow the rear axle to move in every direction imaginable, which is never conducive to traction. Stronger bushings, such as Global West’s Del-A-Lum, Energy Suspension’s polyurethane and Performance Suspension Technology’s Polygraphite bushings, offer freedom of movement yet limit bushing deflection when power is applied.
Perhaps the most common and useful traction tool for leaf-spring cars is the traction bar. Now that you know why spring wrapup causes wheelhop, you can see how the traction bar is used to prevent that from occurring. The bar is usually bolted to the leaf-spring U-bolts at the rearend using a rubber snubber to contact the front of the spring. Ideally, the front snub- ber should contact the leaf spring directly under the front spring eye. Unfortunately, most bolt-on traction bars fall short of the spring eye. While it isn’t absolutely necessary, the short bar can eventually damage a mono- leaf spring.
It’s also very easy to tune a traction bar. Minimizing the air gap between the snubber and the spring allows the bar to “hit” the spring harder and quicker. For a street car, you want at least a ½-inch gap between the snubber and the spring to allow suspension travel. At the track, that gap can be changed with either a taller snubber, large washers under the snubber or angled wedge plates located between the traction bar and the rear axlehousing. Lakewood offers these plates in a variety of angles. If the snubber is too tall, it can easily be trimmed with a hacksaw to create the necessary air gap. It’s also possible to tune traction bars by changing air gaps side to side in order to create preload in the chassis.
Wheelhop is also common in rear-coil-spring cars such as late-model Mustangs and ’64-’72 GM A-body cars and ’78-’88 G-body cars. Coil-spring rear-suspension cars commonly use four trailing arms to locate the rearend and coil springs to support the car. Under acceleration, the rear axle tries to pull the upper trailing arms out of the chassis, putting these bars in tension while attempting to push or compress the lower arms forward. That takes its toll on the stock rubber bushings, leading to axle-tramp conditions especially if the car is raised in the rear.
The easiest and least expensive way to cure wheelhop in a rear-coil-spring car is to first lower the rear suspension until the lower control arm is level and parallel with the ground. That helps return the rear suspension to its proper geometry to help plant the rear tires. It may be difficult if you have large-diameter rear tires, but any effort toward positioning the lower control arms parallel with the ground will help.
Another cure for wheelhop is a stif- fer lower control arm, such as the pieces offered by Global West and Edelbrock/Hotchkis. Global’s tubular-steel lower arm utilizes a Del-A-Lum bushing in the rear position with a spherical bearing in the front bushing location. The spherical bearing prevents deflection of the arm while accurately locating the rearend, even in cornering situations.
Like everything else involved with high-performance cars, suspension tuning is as much an art as it is a science. We’ve only scratched the surface of the different changes you can make to the suspension to optimize e.t. The only way you’ll get there is by going to the dragstrip and trying some of these ideas and then evaluating each one for your particular car. It’ll take time, but your revenge could be a quick car even if you’re down on power.
